The present invention relates generally to agricultural machinery and, more particularly, to an apparatus and method for adjusting the amount of hydraulic fluid forced through a cooler in a hydraulic drive system to improve the efficiency of the cooler.
Standard self-propelled agricultural machines incorporate an internal combustion engine and hydraulic drive systems including at least one hydraulic pump. The engine drives the hydraulic pump, which, in turn, supplies hydraulic fluid to hydraulic motors and/or hydraulic cylinders in the system. It is necessary to maintain the temperature of the hydraulic fluid within a recommended range. To accomplish this, a cooler is included in the hydraulic drive system.
In existing agricultural harvesting machines, a fixed amount of the total quantity of the circulating hydraulic fluid requiring cooling is fed through the cooler before it reaches the fluid tank where it is mixed with the fluid flowing directly back into the tank. The cooler and the quantity of fluid flowing therethrough have to be matched so that the maximum permissible fluid pressure in the fluid cooler will not be exceeded even at the start of work, i.e., when the fluid is cold and, as a consequence, the flow resistance in the pipes is high. Not only is this done to protect the cooler itself, but also to protect the shaft seals in the hydraulic motor and prevent the hydraulic pump from being damaged. However, because the quantity of fluid supplied to the cooler is fixed, the cooler will not be working efficiently when the fluid is hot and the resultant flow resistance in the pipes is lower.
It is an object of the present invention to overcome the deficiencies described above.
An object of the invention is to improve the working efficiency of the cooler by increasing the quantity of fluid subjected to the cooling process but without increasing the cooler""s volumetric capacity or exceeding the permissible pressure in the system.
In accordance with one aspect of the invention there is provided a self-propelled agricultural machine incorporating an internal combustion engine and a hydraulic drive system including a hydraulic pump which is driven by the internal combustion engine and draws hydraulic fluid from a fluid tank to produce a working stream of hydraulic fluid which is returned to the fluid tank, a cooler, and an apparatus for improving the efficiency of the cooler which comprises conduit means for providing a separate circulating stream of hydraulic fluid circulating separately from the working stream of hydraulic fluid and fed back to the fluid tank via the cooler; and a diverting device installed in the separate circulating stream of fluid upstream of the cooler, said diverting device operative for drawing a variable quantity of fluid away from the working stream of fluid into the separate circulating stream of fluid depending on the temperature of the separate circulating stream of fluid.
In accordance with another aspect of the invention there is provided a method for improving the efficiency of a cooler in a hydraulic system of a self-propelled agricultural machine having an internal combustion engine which drives a hydraulic pump for drawing hydraulic fluid from a fluid tank and producing a working stream of hydraulic fluid which is returned to the fluid tank, the method comprising the steps of: producing a separate circulating stream of hydraulic fluid that circulates separately from the working stream of hydraulic fluid and flows from the fluid tank through the cooler, and back to the fluid tank; diverting a partial stream of hydraulic fluid from the working stream of hydraulic fluid to the cooler; and varying the flow of the diverted partial stream of hydraulic fluid
The objects are achieved by creating a separate, advantageously constant, circulating stream of fluid, which circulates separately from the working fluid stream of the hydraulic drive system, to flow from the fluid tank and through a cooler prior to being fed back into the fluid tank and by installing a diverting device, such as a Venturi nozzle, in the constant circulating stream of fluid before the inlet thereof into the cooler, said diverting device drawing a partial stream of fluid away from the working fluid stream for the hydraulic drive system. The size of the partial stream diverted from the working stream depends directly on the temperature of the constant circulating stream of fluid.
The above and other objects, aspects, features and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with accompanying drawings.